"He's very quick, and direct and he's always done well when he's played against us for Ipswich," manager Gary Johnson told City's official website.
Haynes, a 21-year-old midfielder, is expected t make his City bow in the friendly aainst Ajax this week.
Haynes Signs For City
Haynes has joined City for an undisclosed fee and has agreed a three-year contract at Ashton Gate.